Long-range potential centres in disordered solids

Abstract

Measurements are reported on the AC and DC conductivity of evaporated films and single crystals of MoO3. In both cases a frequency-dependent conductivity is observed at low temperatures, and it is established that this is a true bulk property. A model is developed which shows that long-range potential wells surrounding centres such as (O2-) vacancies play a substantial role in the transport process. In particular, DC conduction requires movement of carriers between such wells, while AC conduction can occur within a single well. The resulting difference in the distribution of relaxation times and hopping distances involved can account for inconsistencies between parameters deduced from DC, AC and high-field transport measurements. An improved method is proposed for the calculation of the density of states involved in hopping transport.